Division of Conservation, National Gallery of Art, 4th and Constitution Ave NW, Washington, DC 20565, USA.
Analyst. 2013 Sep 7;138(17):4838-48. doi: 10.1039/c3an00926b. Epub 2013 Jun 25.
In situ chemical imaging techniques are being developed to provide information on the spatial distribution of artists' pigments used in polychrome works of art such as paintings. The new methods include reflectance imaging spectroscopy and X-ray fluorescence mapping. Results from these new methods have extended the knowledge obtained from site-specific chemical analyses widely in use. While these mapping methods have aided in determining the distribution of pigments, there is a growing interest to develop methods capable of identifying and mapping organic paint binders as well. Near infrared (NIR) reflectance spectroscopy has been extensively used in the remote sensing field as well as in the chemical industry to detect organic compounds. NIR spectroscopy provides a rapid method to assay organics by utilizing vibrational overtones and combination bands of fundamental absorptions that occur in the mid-IR. Here we explore the utility of NIR reflectance imaging spectroscopy to map organic binders in situ by examining a series of panel paintings known to have been painted using distemper (animal skin glue) and tempera (egg yolk) binders as determined by amino acid analysis of samples taken from multiple sites on the panels. In this report we demonstrate the success in identifying and mapping these binders by NIR reflectance imaging spectroscopy in situ. Three of the four panel paintings from Cosimo Tura's The Annunciation with Saint Francis and Saint Louis of Toulouse (ca. 1475) are imaged using a highly sensitive, line-scanning hyperspectral imaging camera. The results show an animal skin glue binder was used for the blue skies and blue robe of the Virgin Mary, and egg yolk tempera was used for the red robes and brown landscape. The mapping results show evidence for the use of both egg yolk and animal skin glue in the faces of the figures. The strongest absorption associated with lipidic egg yolk features visually correlates with areas that appear to have white highlights. The results are in agreement with prior site-specific amino acid analysis, underscoring the synergy of both methods. The work here demonstrates that NIR reflectance imaging spectroscopy is a useful technique that can identify and map paint binding media based on differences in chemical composition.
原位化学成像技术正在被开发出来，以提供有关在绘画等多色艺术品中使用的艺术家颜料的空间分布信息。新方法包括反射成像光谱学和 X 射线荧光测绘。这些新方法的结果广泛扩展了广泛使用的现场特定化学分析所获得的知识。虽然这些绘图方法有助于确定颜料的分布，但人们越来越有兴趣开发能够识别和绘制有机绘画粘合剂的方法。近红外（NIR）反射光谱学在遥感领域以及化学工业中已被广泛用于检测有机化合物。NIR 光谱学通过利用中红外区的基本吸收的振动泛音和组合带，提供了一种快速测定有机物的方法。在这里，我们通过检查一系列已知使用蛋彩画（动物皮胶）和坦培拉（蛋黄）粘合剂的镶板画，探索了近红外反射成像光谱学原位绘制有机粘合剂的实用性，这是通过对来自镶板上多个位置的样品进行氨基酸分析确定的。在本报告中，我们证明了通过近红外反射成像光谱学原位成功地识别和绘制这些粘合剂。科斯莫·图拉（Cosimo Tura）的《圣母领报与圣路易斯·德·图卢兹》（约 1475 年）中的四幅镶板画中的三幅都使用高灵敏度的线扫描高光谱成像相机进行成像。结果表明，蓝色的天空和圣母玛利亚的蓝色长袍使用了动物皮胶粘合剂，而红色长袍和棕色风景则使用了蛋黄坦培拉。绘图结果表明，人物的面孔中既使用了蛋黄又使用了动物皮胶。与脂质蛋黄特征相关的最强吸收在视觉上与似乎具有白色高光的区域相关。结果与先前的现场特定氨基酸分析一致，强调了这两种方法的协同作用。这里的工作表明，近红外反射成像光谱学是一种有用的技术，可以根据化学成分的差异识别和绘制绘画结合介质。
